The processing of mail is highly important, and many postal systems are automating their mail-handling facilities. Various automatic machines are known for sorting mail. Machinery is known for handling containers, such as flat trays of mail, as it moves from one location or station within a postal facility to another location for further processing. The container-handling machinery includes buffers which provide delays between the time a container arrives in the general area of a processing station and the time such mail actually arrives at the processing station itself.
The buffers may be in the form of a tower which includes vertically-moving bins, each of which accepts one flat tray or tub of mail. FIG. 1 illustrates a tower 10.
The bins (not illustrated) may move upward or downward, but in any case, provide a delay between the time a flat tray or tub arrives at the input port of the tower, and the time it exits from an output port. This is referred to as "staging" of the flat trays or tubs. Of course, it is disadvantageous to load and unload the towers by hand. Instead, the flat trays or tubs arrive at the input port of the tower on a conveyor device, and likewise leave on a conveyor. In FIG. 1, the mail containers move toward the left on an input conveyor designated generally as 12, enter an input port 10i near the top of the tower 10, and flow from an output port 10o near the bottom of the tower 10 onto a conveyor 14. Mail containers flow from the left end of conveyor 14 to a mail processing station.
The towers, such as tower 10 of FIG. 1, are placed in the vicinity of the mail-processing stations, so as to make the job of moving mail from the tower to the processing station easy for the operator. This requires that an AC power outlet, such as 16 of FIG. 1, be provided near the tower, for powering the tower, as described, for example, in U.S patent application Ser. No. 09/197,628, filed Nov. 23, 1998, in the name of DiSaverio et al. The conveyor 12 associated with the input port of the tower must extend to the mail source tilt tray 18, or possibly a preceding tower.
In order to simplify the installation and control of the towers, they are manufactured as assemblies prior to installation. Since any tower may be used with or without conveyors in various arrangements in which it may be used, the towers as manufactured are arranged for multiple uses. In order to accommodate those situations in which the tower will be used with a conveyor, a port is provided for providing power from the tower to the conveyor. Since there may be a conveyor associated with both mail container ports of the tower, each of the mail container ports may be fitted with such a powering port.
The preferred type of conveyor is one in which direct-current motors are distributed along the length of the conveyor, and these motors are arranged to run or draw power only when a flat tray or tub is located within the region under the influence of the particular motor. Each of these motors or groups of motors is associated with an AC-to-DC converter, for converting alternating source power into direct voltage for the motors and motor controllers.
For reasons of safety, the alternating voltage used to power the AC-to-DC converters along the length of the conveyor is relatively low, and in one embodiment is in the vicinity of 19 volts AC. At this relatively low voltage, load currents are quite large at only moderate loads. For cost reasons, the sources of low AC voltage associated with the various mail container ports of the towers provide only limited current, as for example in the vicinity of 30 amperes. The length of conveyor which can be driven by the low AC voltage and 30-ampere current is limited, and in one embodiment the maximum length of conveyor which can be run is 33 feet. In this particular embodiment, the length of the conveyor which can be powered is maximized by the use of two separate power ports, both at 19 volts AC, each at 15 amperes. One of the two 15A ports drives the first section or portion 12a (about 16 feet) of the conveyor 12, and the second port drives the second half 12b; this arrangement has the advantage of reducing the IR (heating) losses, in the connecting wires to the second half of the conveyor, which are attributable to the current drawn by the first half of the conveyor. In FIG. 1, the two 19-volt, 15A sources are designated 20a and 20b. The first 19-volt power source 20a is connected to a "primary" conductor or bus 22a, which powers the first 3-foot conveyor section 12a1, and also the second 10-foot section 12a2. Section 12a1 is only 3 feet in length, because it is especially made to mate with the tower, and is adaptable for use with a "pusher" which pushes the mail containers into the input port 10i. A bypass cable or conductor 24a is connected to low-voltage supply port 20b at the tower 10 end, and extends to the power 10-foot conveyor sections 12a3 and 12a4 by way of the primary conductor 26a. This arrangement allows the two conveyor sections 12a3 and 12a4 to be powered in a manner in which the IR or resistive drop in the powering conductors 24a and 26a is independent of the current in conveyor sections 12a1 and 12a2.
As a result of the need to locate the tower close to the associated processing station, a conveyor having a length exceeding 33 feet may be required. As illustrated in FIG. 1, the tower also includes a further AC power output port 20c is associated with the mail-handling port 10i. This further AC power output port 20c provides AC power, which may be at the full supply voltage available to the tower, or at some reduced AC voltage. In one embodiment, the full line voltage available to the tower is 208 volts, and the reduced line voltage at port 20c is 120 VAC. The available AC power at the further AC port 20c is coupled by a path 28 to a location at the end of first 33-foot section of conveyor, at which location a transformer 30 converts the 120 VAC to 19 VAC, for powering a further 40-foot section 12b of conveyor 12. Transformer 30 does not receive power from primary conductor 26a, and bypass conductor 24a' is not powered at all, since conveyor sections 12a3 and 12a4 are powered by primary conductor 26a.
Conveyor section 12b includes two 10-foot sections 12b1 and 12b2, which are powered by low-voltage AC from transformer 30 by way of primary power conductor 22b. Power is fed to primary conductor portion 26b from bypass conductor portion 24b. Sections 12b3 and 12b4 of conveyor 12b are powered by primary conductor portion 26b. Bypass conductor portion 24b' is not powered. Thus, the total length of conveyor 12 which can be powered from the tower is 73 feet.
FIG. 2 is a simplified representation of one ten-foot section of conveyor 12 of FIG. 1. For definiteness, the section illustrated is chosen to be section 12a3, but all of the section are identical (except for the three-foot section 12a1, which is shorter in axial length). In FIG. 2, a pair of support side rails 210.sub.1 and 210.sub.2 extend parallel with each other, and support a set of rollers, one of which is designated 212. The power rollers are controlled in sets of four, so each subsection of conveyor 12a3 contains four power rollers. Each power roller may drive additional slave rollers by means of gears or belts. The power rollers are powered by direct-current motors associated with power cards mounted on the siderails 210.sub.2. In FIG. 2, the four power cards (PC) are designated 212a, 212b, 212c, and 212d. A power supply designated as 214 is coupled to primary bus 26a. The bypass bus 24a' simply extends along the side rail 210.sub.2, and terminates at connectors 240.sub.1 and 240.sub.2. Primary bus 26a is terminated at the left end at a connector 260.sub.1 and at the right end at a connector 260.sub.2. It should be noted that busses 24a' and 26a are multiconductor sets, rather than single conductors; in a preferred embodiment, each bus contains two power conductors and a ground conductor. Conveyor sections such as that described in conjunction with FIG. 2 are sold by Siemens ElectroCom. In normal use of conveyor sections such as that of FIG. 2, two kinds of electrical connections are made. The first type of electrical connection is that which is used when the conveyor section is adjacent the source of low-voltage AC for that conveyor section, and includes coupling both the primary connector 260.sub.1 and the bypass connector 240.sub.1 to the source 320 of low-voltage AC. Those conveyor sections more distant from the source 320, but still near the source of low-voltage AC, have their connectors 260.sub.1 connected to connector 260.sub.2 of the first conveyor. Those conveyor sections more remote from the source of low-voltage AC will have their connectors 260.sub.1 connected to connectors 240.sub.2 of the electrically-earlier conveyor. The conveyor most remote from the source of low-voltage AC will not have any further connections to its connectors 240.sub.2 and 260.sub.2.
Improved tower conveyor arrangements are desired.